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2009ApJS..182..216K - Astrophys. J., Suppl. Ser., 182, 216-309 (2009/May-0)
Structure and formation of elliptical and spheroidal galaxies.
KORMENDY J., FISHER D.B., CORNELL M.E. and BENDER R.
Abstract (from CDS):
Besides extra light, we find three new aspects to the ("E-E") dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have Sérsic indices n > 4 uncorrelated with MVT. They also are α-element enhanced, implying short star-formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n ≃ 3±1 almost uncorrelated with MVT and younger and less α-enhanced stellar populations. These are new clues to galaxy formation. We suggest that extra light ellipticals got their low Sérsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering.
We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E-E dichotomy arose. If energy feedback from active galactic nuclei (AGNs) requires a "working surface" of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation.
Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae.
In an appendix, we develop machinery to get realistic error estimates for Sérsic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from Sérsic fits.
Abstract Copyright: ∼
Journal keyword(s): galaxies: elliptical and lenticular, cD - galaxies: evolution - galaxies: formation - galaxies: nuclei - galaxies: photometry - galaxies: structure
VizieR on-line data: <Available at CDS (J/ApJS/182/216): galaxies.dat table3.dat>
Simbad objects: 72
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